NavajoCEO: What is going to happen to the collection of Bethesda games Gog sells? The Microsoft Bethesda buyout. They going to be pulled?
No one can answer that question, as that would require mystical powers to see into the future.
But it's certainly highly possible that they could be pulled in the future.
In fact,
any & every game that is on GOG could be pulled in the future. There is no guarantees that any of them will stay 100% for sure for all-time. Nor that GOG itself will stay for all-time.
So if you are worried about such things, then yes, you must backup all your games.
And having only one backup isn't secure either by the way, because the backup source could become defective, or there could be a fire or flood that destroys it, or something like that.
So the safest possible method would be to have multiple different backups, and not all stored in the same physical location, and with some of them stored in Cloud storage.
Grargar: I doubt Microsoft would cancel existing contracts for no good reason
But they wouldn't need to "cancel existing contracts" in order for the games to be pulled from GOG. Rather, they'd need only to let them expire, and then choose not to renew them again...which is a very likely possibility.